Seeds are often treated to reduce yield losses during cultivation and for enhancing the agronomic and nutritional value of the produce. Such treating agents are for example fungicides, insecticides, rodenticides, nematocides, miticides or bird repellents. Furthermore, many varieties of genetically altered crops are coming to the market. Treated and/or genetically modified seeds must be marked in order to distinguish them from the untreated and unmodified seeds. The marking of seeds is particularly beneficial for farmers who then can easily distinguish the chemically treated and modified seeds for plantings from e.g. cereal grains for consumption.
A number of patents describe processes for the marking and coating of seeds by active ingredients and film forming compositions. U.S. Pat. No. 5,087,475 discloses a process for the film coating of materials using a water- and gas-permeable, adhesive film-forming substance, which consists of spraying the film-forming substance on seed materials and drying the seed materials. The spraying and drying steps are carried out simultaneously using a compact volume of seed materials in motion. The film-forming substance is supplied in the form of a solution or a suspension. U.S. Pat. No. 5,470,581 discloses a process for providing an aqueous film coating from a combination of maltodextrin and cellulosic polymers for pharmaceutical tablets, candy, cereals and agricultural seeds. The aqueous suspension can be applied by spraying. The aqueous suspension can contain a colorant. U.S. Pat. No. 5,849,320 discloses a process for coating a seed with an insecticide.
U.S. Pat. Nos. 4,853,429 and 4,881,343 describe an aqueous medium containing a dye or pigment and a binder resin composed of the salt of chitosan and an organic acid for seed coloring. The patents indicate that the colorant is used at a concentration of about 0.1 to 10% by weight based on the aqueous medium and exemplifies using C.I. Pigment Green 7, C.I. Pigment Green 128 and C.I. Pigment Red 122 at 2.5% concentration. The patents do not indicate the form or solids content of said pigments.
U.S. Pat. No. 5,746,022 discloses a seed color coating using a poly oxyalkylene substituted chromophore in the coating. The coating composition contains a solvent, binder, colorant and other optional additives. The coating composition is applied as a film coating by spraying a solution, dispersion and/or suspension onto the seeds. The aqueous-based coating composition is described as containing 5 to 80 parts biologically active agents, 20 to 45 parts water, 1 to 15 parts binder and 0.1 to 50 parts colorant. In Example 11, the coloring composition consists of 310 parts lime, 170 parts water, 30 parts poly (vinyl alcohol) binder and 1 part of green colorant (37% solids).
U.S. Pat. No. 4,272,417 discloses a liquid seed coating composition containing a binding agent, an active ingredient and a coloring agent in a liquid medium including water and a polyol. The suggested colorants are selected from dyes, pigments and lakes. The coloring agent is selected for solubility and/or dispersibility in the liquid system. The patent does not disclose any means for producing a so-called dispersible pigment. The coloring agent is present at between 0.1 to 3 percent by weight, preferably 0.4 percent by weight of the total composition. The solids content of the colorant is not provided.
U.S. Pat. No. 4,368,591 discloses seeds that are coated with an active ingredient and between 0.035 and 1.8 grams of titanium dioxide per kilogram of seed in either rutile or anatase form. The titanium dioxide allegedly provides a bright, opaque coating on the seeds. The active ingredient and particulate titanium dioxide are applied onto the seeds in an aqueous medium. The particulate titanium dioxide is in dispersion in the aqueous medium. The dispersion contains between 10 and about 100 grams of insoluble titanium dioxide per liter of dispersion.
U.S. Pat. No. 5,137,747 claims a process for drying a germinative substrate of grains or seeds which have been wetted in a coating or surface film forming treatment by dusting the substrate with a desiccant powder consisting of at least one alumina silicate and which is substantially free of components which would interfere with germination of the substrate. Although these desiccant powders can contain pigments due to the high alumina silicate content they tend to be low in coloring strength.
Published PCT application WO 99/66784 discloses a process for coating seeds with a thin coating of a pigment that selectively allows light rays having wavelengths of about 570 to 700 nm to pass there through, or, in the alternative, selectively reflects light rays having wavelengths of about 420 to about 520 nm. The applicants exemplified seeds that were coated with a red pigment, which reflected approximately from 600 to 700 nm, a blue pigment, which reflected approximately 400 to 500 nm, and a green pigment, which reflected approximately 500 to 570 nm. The green pigment produced the greatest budding ratio with respect to the selected seed. The application does not provide any showing of a control set of seeds in order to assess improvement without any pigment coating.
Even though the known processes can deliver marked seeds, they are often environmentally unfriendly since they use aqueous dyes which can cause colored effluents. Most commercially available organic pigment particles are not wettable in aqueous mediums and require the addition of surfactants or hydrophilic copolymers. However, current seed coloring systems have also employed coating compositions that contain aqueous pigment dispersions, which have a low solid pigment concentration. Despite the presence of surfactants, the aqueous dispersions of pigment can settle out as function of time. Additionally, such surfactants can have a negative impact on the growth of the seeds or can negatively interact with other active coating ingredients generating an undesirable gel. Furthermore, aqueous pigment dispersions, delivered in drums need a large, and in winter, heated storing area to avoid freezing.